1. Field of the Invention
The apparatus of the present invention relates to an apparatus for injecting tubing down a pipeline, well or open hole. More particularly, the present invention relates to a bi-directional thruster pig apparatus which is capable of injecting coiled tubing down a pipe in deep water to provide service to the pipe in order to remove blockages such as paraffin, hydrates, scale or solid debris. The pipe in question may be part of a vertical or horizontal well, pipeline or a combination of both. More particularly, the apparatus and method of the present invention provides a bi-directional thrust system by using changeable, adjustable check valves that are double acting in each direction, the amount of hydraulic thrust pressure being set and predetermined prior to the job or changed in the fields. The bi-directional fluid flow feature of the apparatus allows the apparatus to be retrievable from the pipeline after it has completed its cleaning function by eliminating or reducing any hydraulic or hydrostatic force against the pig as it is retrieved from the pipeline or well.
2. General Background of the Invention
Drilling for and producing subterranean oil and gas deposits and seeking out other energy sources, it is necessary to drill either vertical, horizontal, curved or a combinations of such, and then to insert an elongated tube from the surface deep into a pipe or the open hole. Such drilled holes may be part of, for example, a well, pipe line, production line, or drill pipe, depending on the circumstances. Quite often it is necessary to insert a tube, whether it be continuous or segmented into the pipe or open hole, the tube having a diameter smaller than the diameter of the drill, production pipe or open hole, in order to remove or destroy blockages which have formed in the pipe or drilled hole.
It has become very beneficial in the cleaning or clearing of pipelines, or horizontal holes to utilize a continuous tubing, referred to as coiled tubing. The tubing is usually injected type tubing which is relatively flexible, and is of a continuous length being rolled off a large reel at the rig site and down hole. Various types of tools may be connected to the end of the coiled tubing to undertake whatever task is required below the surface. Coil tubing strings can be joined together up to and exceeding ten miles at a time.
Large forces are often necessary to insert and withdraw thousands of feet or more of steel tubing into a pipe or open hole which may be filled with hydrocarbons or other materials. Most apparatuses focus on the injector head located where the smaller tubing is injected into the larger tubing. The injector head grips the tubing along its length and, in conjunction with a motor, guides and forces the tubing into the pipe via, for example, a dual, opposing gripper chain or conveyor belt on the surface of the well. Injector heads are quite common in the oil and gas art, as found, for example, in U.S. Pat. Nos. 3,827,487; 5,309,990; 4,585,061; 5,566,764; and 5,188,174, all of which are incorporated herein by reference.
A common problem found in the art of injecting coiled tubing down a pipeline is that the tubing may be bent or kinked, i.e., the tubing becomes helical, down the well due to the large forces pushing against it and the weight of the tubing itself. Furthermore, as the pipe becomes more horizontal, the weight of the coiled tubing itself no longer acts as a force pulling the tubing along, and instead acts against the wall of the pipe, creating friction. In addition, the weight of the tube no longer acts to straighten the coiled tubing, and the coil encourages coiling in the pipe. Such a coil, coupled with friction, results in increased force between the coiled tube and the inner diameter of the pipe, and this effectively binds the tubing. As a result of this and other problems, such prior art devices cannot effectively insert more than about 3,000 to about 5,000 feet (900 to 1500 meters) of tubing in substantially horizontal pipe.
Other methods have been employed to increase the length to which tubing can be injected. U.S. Pat. No. 5,704,393, describes an apparatus that can be set in the well at the end of the coiled tubing string at a determinable location. The apparatus is a valve apparatus, a packer apparatus, and a connector. Seals are provided that allow the coiled tubing, but not fluid, to move in a centrally located bore through the packer apparatus. The apparatus is immobile against the outer pipeline, and has the ability to restrict or prevent fluid flow. Once the packer is set, the annular pressure, i.e., the pressure differential between the pipeline and the interior of the coiled tubing, is increased by injecting fluid into the annular volume. This increased pressure stiffens and straightens the coiled tubing, allowing for increased distance of injection of coiled tubing into the pipeline.
Further, U.S. Pat. No. 6,260,617 issued Jul. 17, 2001 entitled “Skate Apparatus for Injecting Tubing Down Pipelines,” teaches a device which is intermittently placed along the length of the coil tubing, and having a plurality of roller members which allows the coil tubing to be maintained within the center of the pipe in order to reduce the friction between the coil tubing and the pipeline. However, over large distances over two or more miles, such a device is still not suitable.
All of the aforesaid problems confronted in the art of using coiled tubing down a borehole or pipeline can be found in related U.S. Pat. No. 6,315,498, entitled “Thruster Pig Apparatus For Injecting Tubing Down Pipelines,” which is incorporated herein by reference. This patent discloses a method and apparatus for inserting and withdrawing coiled tubing from pipe to avoid bending or twisting of the coiled tubing at great distances downhole. There is provided a thruster pig that utilizes pressure differential across the thruster pig to generate force needed to inject the tubing down the pipeline. The pig includes one or more chevrons to impede fluid flow around the pig, so the pig can be pressured at its rear to move down the pipeline. There is provided an opening for allowing fluids pumped down the center of the tubing to pass to the front of the pig. There is further provided one or more valves in series or in parallel that slow the fluids to pass through the pig to the annulus behind the pig. There are a second set of check valves for allowing fluids under some conditions to flow from the annulus between the tubing and the interior surface of the pig to the front of the pig. These valves are limits of the pressure that can be exerted against the back of the pig, and will open to allow fluid to pass, principally when the pig is being withdrawn from the pipeline. This device, although effective, cannot be operated to allow the device to continue to simultaneously move forward in the pipeline while obstructions in the pipeline are being cleaned away. Also, unlike the present invention, the fluid under pressure is being injected through the bore of the coiled tubing through a single nozzle at the forward end of the pig, which limits its movement and cleaning ability in the pipeline. Also, there is no provision in this device to allow pieces of debris to flow up to the surface behind the pig, as the pig moves forward to destroy the obstructions in the pipeline.